Default

For applications that do not require standard-conforming behavior (those that use the
socket interfaces described in section 3N of the reference manual; see Intro(3)
and standards(5)), the following may be declared as functions, or defined as macros,
or both:

Standard conforming

For applications that require standard-conforming behavior (those that use the socket interfaces
described in section 3XN of the reference manual; see Intro(3) and standards(5)),
the following may be declared as functions, or defined as macros, or both: